In packet networks, non-real-time data signals and real-time data signals, such as voice, video, and audio, can be encoded with error correcting codes prior to being packetized and transmitted across the packet network. This can be accomplished through various forward error correction (FEC) schemes. In general, FEC schemes introduce sufficient redundancy in the signal (or message) to be sent so that packets lost or corrupted during transmission can be reconstructed at the receiver. In other words, the purpose of FEC is to improve the capacity of a channel by adding some carefully designed redundant information to the data being transmitted through the channel. The encoding of signals with error correcting codes can protect a transmitted signal against packet losses, packet erasures, bit errors, and also packet delay in the case of real-time signals.
At the receiving end of a transmission that has been encoded with an error correcting code and packetized, the arriving packets are typically first placed in a packet-receiving buffer (or ‘playout’ buffer). According to a ‘pipelined’ process, the buffered packets are read out (or ‘played-out’) of the buffer periodically, the bits or frames are extracted from the packet payloads, the bits or frames are decoded using a decoding method that corresponds to the encoding method that has been applied at the transmitting end prior to packetization, and the decoded digital signal is played-out to the receiving entity (a device, process, or person). Packets that arrive at the packet-receiving buffer when the buffer is already full, or, in the case of real-time signals, after a scheduled (or required) playout time has passed, may be discarded. The discarding of late packets causes the loss (or erasure) of the bits or frames contained in the late packets. The discarding of late packets is in addition to any packet loss, packet erasure, or packet corruption that may have already taken place in the packet network.
Bits or frames that are erased or lost may be indicated to the decoder, and the decoding method applied to the received bits or frames may correct erased, lost or corrupted bits or frames. However, even with FEC schemes in place, errors still occur in the decoding process. Therefore, systems and methods are still needed for improving the performance (i.e., the bit error rate) of forward error correcting codes.